3c905B fast on NT, slow on Linux

[Woodford, Paul]

I have a dual boot box with a 3c905B.  When I boot into NT, I get good
performance with the card.  Transferring a 128 MB file takes 12-20 seconds.
When I am in Linux, however, the performance is really slow; a 128 MB file
will take about a minute.  The hardware doesn't change at all; same card,
same wires, etc.

During boot I get:

3c59x.c:v0.99H 11/17/98 Donald Becker
http://cesdis.gsfc.nasa.gov/linux/drivers/vortex.html
eth0: 3Com 3c905B Cyclone 100baseTx at 0xb800,  00:10:4b:14:c2:88, IRQ 18
  8K byte-wide RAM 5:3 Rx:Tx split, autoselect/Autonegotiate interface.
  MII transceiver found at address 24, status 786d.
  MII transceiver found at address 0, status 786d.
  Enabling bus-master transmits and whole-frame receives.
The results from cat /proc/net/dev are:

Inter-|   Receive                                                |  Transmit
 face |bytes    packets errs drop fifo frame compressed multicast|bytes
packets errs drop fifo colls carrier compressed
    lo:  111517     812    0    0    0     0          0         0   111517
812    0    0    0     0       0          0
 dummy:       0       0    0    0    0     0          0         0        0
0    0    0    0     0       0          0
  eth0:374227954  767941  679    0    0  1037          0         0 963264949
878331    0    0    0     0       0          0
I experimented briefly with 0.99L, but it didn't seem to help.  Any ideas?
Is there any further information I should look at?  I have vortex-diag and
mii-diag, but I don't know what to do with them.

Paul Woodford